Babies Motor Better with Breast Milk

Physicians have been advocating for years that breast milk is the best food for infants. Not only does it have the nutrition that babies need, but it also provides some antibodies and growth factors that speed maturation of the infant gut, thereby fending off disease. Now, a team of scientists in Britain offers strong evidence of another benefit. Mother's milk boosts early neurological development.

Social epidemiologist Yvonne J. Kelly of University College London and her colleagues were aware of studies that had suggested neurological benefits from breastfeeding. However, notes Kelly, those earlier analyses tended to be small and done in special populations—such as preemies. They also failed to rule out many factors that might account for differences in a child's developmental skills. Among such possible confounders: race, parent's education, family income, parenting attitudes, depression in the mother, characteristics of childcare, or the baby's overall health.

Kelly and her coauthors had access to information on such features for the families of 18,000 infants from throughout the United Kingdom. The scientists also had motor-development data from in-home interviews with the families of those children when each baby was between 8 and 11 months old. The data were collected as part of the still-ongoing Millennium Cohort Study begun in 2000.

Among these children, 9 percent exhibited gross motor delays, which means being late in reaching such major milestones as sitting up, proficient crawling, or standing. Six percent also showed delays in fine-motor coordination—such as clapping hands, transferring an object from one hand to another, or efficiently using the thumb and forefinger like pincers to pick things up. Only 1 percent of the infants showed both types of delays, the scientists report in the September Pediatrics.

When the researchers began their work, they were skeptical of a link between breastfeeding and motor skills. "Although we thought we'd initially see some kind of effect, we had expected to be able to later explain it all away when we [adjusted for] covariants," such as a family's income or mother's mental health, Kelly says.

To the researchers' surprise, Kelly notes, children "were about 50 percent less likely to have a [developmental] delay if they had prolonged, exclusive breastfeeding when compared to those who were never breastfed." They defined breastfeeding as prolonged when it had lasted at least 4 months. Even babies receiving mother's milk for a short while—2 months or less—were 30 percent less likely to have a developmental delay than those who received solely infant formula, beginning right after birth.

A child's motor coordination was compared against others of the same age in months and categorized as exhibiting a developmental delay if he or she lagged behind 90 percent of the other infants that age.

The link between delays and being formula fed was robust, Kelly told Science News Online. "We put everything including the kitchen sink in there in terms of adjusting for explanatory factors," she says, and the link between the developmental delay and lack of breastfeeding "was not attenuated at all."

By contrast, a roughly 30 percent delay in the fine-motor coordination that the team initially calculated for the formula-fed babies disappeared after such adjustment for possible confounding factors.

The Institute of Medicine of the National Academies in Washington, D.C. encourages 4 to 6 months of exclusive breastfeeding (see Honey, Let's Shrink the Kids). Current recommendations in the United Kingdom for infant feeding call for "6 months of exclusive breastfeeding, in line with World Health Organization recommendations," Kelly's group notes.

In practice, breastfeeding rates are low. In the new study, which considered a representative cross-section of the UK population, 34 percent of the infants were never breastfed, and only 3.5 percent were still breastfed at 4 months. The average period that babies were breastfed was 4 weeks.

"I'm not a breastfeeding evangelist in any way, shape, or form," says Kelly, herself a mother of three. "If breastfeeding works for the mother-infant pair, fine—because it's almost a universal good." However, she recognizes that some children refuse breastfeeding, and in other instances, a mother can't nurse her baby for any of various reasons.

Kelly's group would now like to know how long breastfeeding's neurological advantage persists. The team has just received data on motor skills for the same children, collected when each youngster was about 3 years old. The researchers plan to sift through it to see whether breastfeeding had conferred any coordination benefits or other neurological advantages on these preschoolers.